Window panes with adjustable transparency are a known product. For example, see U.S. Pat. Nos. 6,674,419, 6,597,412, 6,522,446, 6,606,185, 6,301,040, EP 0 608 203 B1, and Document BINE 1/02, published by the Technical Information Center Karlsruhe, Gesellschaft fur wissenschaftlich-technische Information mbH, as well as the Internet site www.smartglass.com. Window panes with an adjustable transparency can be obtained, for example, from FLABEG GmbH & Co. KG, Siemenstrasse 3, 90766 Furth, Germany, or GESIMAT GmbH, Gesellschaft fur intelligente Materialien and Technologien, Innovationspark Wuhlheide, Kopenicker Strasse 325, 12555 Berlin, Germany.
Another example is the electrochromic automatic-dimming rear view mirror of Gentex, http://www.gentex.com/, which detects and eliminates dangerous rearview mirror glare.
All the above use either electro-chromic materials or liquid crystals serving as the active material, and their activation is carried out by electric voltage, applied across the active material through transparent electrodes.
There is a constant need for simpler active transparency control of windows, mainly for display showcases, vehicle front windows, sun protectors and regulated sun glasses.